The present invention relates to a power tong apparatus for making and breaking threaded connections between lengths of small diameter tubing. Make-and-break apparatus have long been used in the oil and gas producing industry to grip and rotate lengths of well pipe during the making up or breaking out of joints of such pipe. Make-and-break apparatus usually comprise two tongs operating in conjunction with each other: a backup tong which serves to grip and hold stationary the length of pipe which extends into the well and a power tong which serves to grip and rotate the length of pipe which is suspended in the derrick above the well. In operation the backup tong prevents the lower length of pipe from being rotated while the upper length of pipe is being screwed into or unscrewed from the lower length of pipe by the rotating power tong.
Power tongs may be of either the "open" head type or the "closed" head type. The "open" head type power tong possesses a hinged bull gear and gate in the side of the structure enclosing the pipe which opens to permit the power tong to encircle the pipe from the side. The hinged bull gear closes upon the pipe once the power tong has been placed around the pipe. The "closed" head type power tong possesses no side openings. It is generally in the form of a ring through which the pipe ends must be inserted and through which the pipe lengths must be guided.
Power tongs may be designated to rotate pipe in only one direction or may be designed to rotate pipe in either of two directions. Power tongs capable of bi-directional rotation permit the threaded ends of the pipe to be screwed together and then unscrewed without turning over the power tong. A power tong capable of rotating pipe in only one direction would need to be turned over to rotate the pipe in the opposite direction.
Closed head type power tongs capable of bi-directional rotation in many instances require a manual change of pipe gripping elements in order to reverse the direction of rotation. This requires removal of the cover of the power tong, the removal, inversion and replacement of each pipe gripping element in the power tong and replacement of the cover of the power tong.
While many types of power tongs have been developed over the years, the designs of these power tongs have been directed primarily toward the larger types of well pipe, such as tubing, casing, and drill pipe larger than 23/8" O.D. The design of the present invention is concerned with a power tong adapted for use on very small diameter pipe (1.66 inch outer diameter or smaller). Such small diameter pipe is generally referred to in the oil and gas producing industry as macaroni tubing and is typically used in snubbing and hydraulic workover operations.
The small diameter of such macaroni tubing presents practical problems in designing a power tong to supply the appropriate amount of gripping force and torque. The relatively small surface area of the tubing presents a very limited area with which the gripping means of the power tong can make contact. Also, the small diameter of the tubing provides a very short radius or lever arm to provide torque. Care must be taken that the gripping strength of the power tong is not concentrated on too few points on the tubing. Otherwise, the relatively low rigidity and strength of the thin walled tubing will be overcome and the tubing will bend, buckle or otherwise deform. While meeting this requirement, the power tong must be able to apply sufficient torque to screw and unscrew very small diameter tubing without slipping and damaging the pipe.